Metal roller chains have recently come into increasing use as power transmission media, especially in automobiles, where higher loads, and the demand for high speed, maintenance-free, operation have caused the roller chain to displace the toothed belt.
As shown in FIGS. 5(a), 5(b) and 5(c), a conventional roller chain 500 comprises an inner link 520 (FIG. 5(b)) in which both ends of each of two cylindrical bushings 522 are fixed, by press-fitting, in bushing holes 526 in a pair of inner plates 524, and rollers 528 fit rotatably on the bushings 522. An outer link 540 (FIG. 5(c)) has two pins 542, which extend through the bushings and are similarly fixed, by press-fitting, in holes 546 in a pair of outer plates 544 disposed on the outsides of the pair of inner plates 524, as shown in FIG. 5(a).
From the standpoint of size balance, the roller chains most commonly used are “A type” roller chains, having the relationships 0.591≦D/P≦0.640 and 0.281≦d/P≦0.377, and “B type” roller chains, having the relationship 0.575≦D/P≦0.670 and 0.288≦d/P≦0.389, where D is the outside diameter of the roller, d is the outside diameter of the pin, and P is the pitch of the roller chain. (See JIS B1801).
The are two reasons for these limitations. When D/P is too high, the sprocket teeth engaging the roller chain are too narrow and insufficiently strong. On the other hand, when D/P is too low, the outside diameter d of the pins becomes too low, resulting in a reduction of the strength of the chain.
A B-type roller chain, designated a “06B” chain according to JIS B1801 (coincident with the ISO number) has been used commonly as a power transmission medium in an automobile engine. This chain has a pitch of 9.525 mm, an outside roller diameter of 6.35 mm, and an outside pin diameter of 3.28 mm,
It has been reported that, when the above-mentioned conventional roller chains are used as timing chains in automobile engines in which high loads, for example 4 kN, are encountered, some of the roller chains do not exhibit the expected endurance. Therefore, enhancement of reliability of the engine and of the endurance of the roller chain, has become an urgent problem. As a result of continued study, we have found that the “elongation—wear resistance” of a roller chain is exceeded when a high speed engine applies an unexpectedly high load to the pins of the roller chain. The conventional ratio of the outside diameter D of a roller, to the pitch P, and the conventional ratio of outside diameter d of the pin to the pitch P (D/P and d/P), which were set in accordance with the conventional size balance, are not always the optimum values.
The general object of the invention is to solve the above-mentioned problems encountered in a conventional roller chain, and to provide a roller chain with enhanced wear resistance and strength, and particularly good endurance when the roller chain is used as a timing chain in an automobile engine which rotates at high speed.